Luminescent material



' March'26, 1940. b L 2,195,341

LUMINESCENT MATERIAL Filed May 14,-1936 Invent I "b W x M "$Attorney;;

notation of New York App]! Patented Mar. 26, 1940 PATENT orrlcl-i aleasu Lumasomrrm'maun John Turton mam, Harrow wean, England,

assignor to General Electric Company, a corcation May 14, 1936, semi No. 79,761 in Great Britain May 22, 1935 A 4 Claims. (01. 250-81 This invention relates to electric lamps comprising an electric discharge (more particularly through low pressure mercury'vapour) and luminescent materials excited by the ultra-violet 5 radiation and/or slow electrons from the 'discharge.

One of the best known luminescent materials is zinc silicate.

In its usual form, known as willemite, it fluoresces with a green colour; the composition of willemite is believed to be 2ZnO.SiOz, containing a trace of manganese. I

have discovered that there is another form-of I zinc silicate, having a crystal structure different from that of willemite, which (when associated as usual with a suitable activating impurity) luminesces yellowish white when excited by contact with a mercury discharge. I believe that the main constituent of this form has the composition ZnO.2SiO2; but I prefer to identify it by its crystal structure as revealed by X-ray analysis.

I have not yet obtained crystals large enough for the complete determination of the spacegroup; but the following two tables of X-ray spacings serve for identification. Table I is the X-ray spacings of my yellowish white luminescing zinc silicate and Table H is the X-ray spacings of the well known green fluorescent zinc silicate. In both tables the first column represents the distance in Angstroms between crystal :0 planes from which X-rays are reflected with a relative intensitygiven'in the second column. In this second column s. rep m medium, v. ve

Table I resents strong, w. weak,

pacing (1.).

Intensi y doublet) sass? Table II Spacing (1.) Intensity can secs W. S. W W W It will be understood by those skilled in the art that it is not possible at the present stage to I be certain that some of the weak spacings are not due to inessential impurities and are not therefore characteristic of the material in question.

My invention thereforecomprises an electric lamp wherein a material whose main component contains zinc, oxygen, and silicon arranged in a crystal structure characterised by X-ray spacings substantially as in the foregoing table, is excited to luminescence by an electric discharge device relative to which the said material is located so that it is subjected to the ultra-violet radiation from the said discharge in the said device. Of course the usual way to expose a material to these agencies is to coat it on the interior surface of the envelope of the discharge device. The

discharge device is preferably one adapted-to emit the mercury spectrum, and particularly the "low pressure spectrum.

The impurity whose presence is associated with the yellowish-white luminescence may. be manganese. The possibility ofother impurities in addition or substitution is not excluded.

In one method of preparing the material characterised by the foregoing table, zinc oxide and silica are mixed in the molecular proportions ZnO:2SiOa. Both must. be extremelyipu're. The silica should be in the form of gel, which may be prepared by precipitating very pure potassium silicate with hydrochloric acid. To the mixture is added manganese nitrate in'such proportion that metallic Mn forms about 0.1% of the whole mixture.

The paste so formed is dried in air at 180 0., reground, and then heated in a silica' boat in air at 850 C., preferably for a period as longas 15 hours; In general I have foundthat the longer the heating, the brighter the 1c of th product. Itis not essential that there should be in the product no excess of znO nor of SiOa.

Small excess of SiO: particular may be perglass envelope l filled with rare gas at a presmltted.

Thezinc silicate material characteristic of the invention may be used in conjunction with other luminescent materials and in any of the ways well-known in the art for using materials excited by ultra-violet radiation and /or slow electrons.

The accompanying drawing shows somewhat conventionally an electric lamp. embodying the present invention; At either end of a tubular sure of a few millimetres electrodes 2 and 3 are mounted. A thin layer 4 of zinc silicate, made according to the foregoing specification, isdeposited on the inner surface of the cylindrical part ofthe envelope; and a globule 5 of mercury from which vapour is generated is contained within the envelope.

I claim:

1. The method of manufacturing a fluorescent material which comprises mixing 'purezinc oxide and pure silica. in the molecular proportions ZnOzZSiOz, adding to the mixture a manganese compound in-solution, drying the resulting paste, regrinding the dried product, and heating the resulting material, to about 850 C. v

2. The method bf manufacturing a fluorescent material which comprises mixing pure zinc oxide and pure silica in the 1rno1ecular proportions Zn0:2Si0z, adding to the mixture amanganese compound in solution and in such proportion that metallic manganese forms about 0.1% of the whole mixture, drying the resulting paste, regrinding the dried product, and heating the. resulting material to about 850 C.

3. A luminescent material emissive in the yellowish-white spectral range, said material containing zinc,'oxygen, and silicon arranged in a crystal structure, characterized by the following X-ray spacings:

and containing also an activating impurity.

4. A luminescent material emissivein the yellowish-white spectral range, said material con- 1 I taming zinc, oxygen and silicon arranged in a crystal structure characterized by the- X-ray spacings set forth in claim 3 and containing manganese as the activating impurity.

JOHN TURTON RANDALL, 

